1. Field of the Invention
The present invention generally relates to a rotary knife assembly which is coupled with another rotary knife assembly to provide a pair of upper and lower rotary knife assemblies, and in particular to the technique for producing contact pressure between the upper and lower knives.
2. Prior Art
FIG. 1 depicts a conventional rotary knife assembly, which includes an annular rotary knife 1 securely fitted on a rotary shaft 2 through a flange 3. The flange 3 includes a flange portion 4 disposed at one end thereof and having a diameter greater than the other end of the flange. A pressure oil chamber 5 is formed in the flange 3 so as to be disposed adjacent to the inner peripheral surface thereof and extends along the entire circumference thereof. Formed in the flange 3 is a radially extending bore 6 which opens at the outer end to the outer peripheral surface of the flange 3 and is communicated at the inner end with the pressure oil chamber 5. A piston 7 is sealingly fitted in the bore 6 for sliding movement therealong, and an end member 8 is securely fixed to an opening end of the bore 6. A screw member 9 is threadedly engaged with an internally threaded aperture of the end member 8 to urge the piston 7 radially inwardly of the flange 3. The rotary knife 1 is first fixed to the flange portion 4, and then the flange 3 is fitted on the rotary shaft 2. Subsequently, the screw member 9 is tightened to cause the piston 7 to move radially inwardly of the flange 3, and thus an operating oil is pressurized into the pressure oil chamber 5 to bring the inner peripheral portion of the flange 3 into abutting engagement with the rotary shaft 2, whereby the flange 3 is securely fixed to the shaft 2.
Two rotary knife assemblies, each of which is constructed according to the aforesaid assembly, are arranged to provide a pair of upper and lower assemblies, and are utilized for cutting sheets of various materials.
In the rotary knife assemblies as described above, however, the upper and lower knives are arranged with a prescribed clearance formed therebetween, and hence it is impossible to cut a thin sheet of material such as a synthetic resin film. Accordingly, there have been developed rotary knife assemblies as disclosed in FIGS. 2 to 4.
The rotary knife assembly as shown in FIG. 2 includes a rotary shaft 10 having a flange portion 10a and an externally threaded reduced-diameter portion 10b. A plurality of flange members 11, each of which is provided with an annular disc-shaped rotary knife 12, are fitted on the shaft 10 in series in such a manner that the flange 11 arranged at one end is disposed adjacent to the flange portion 10a with a collar 13 interposed therebetween, and a nut member 14 is threaded on the reduced-diameter portion 10b with a collar 15 interposed between the nut member 14 and the flange 11 arranged at the other end, whereby the flanges 11 are securely fixed to the rotary shaft 10. Each rotary knife 12 is fitted on a reduced-diameter portion of a respective flange 11 for sliding movement therealong, and a belleville spring 16 is disposed around the reduced-diameter portion of the flange for resiliently pressing the rotary knife 12 in a direction away from a flange portion of the flange 11.
In operation, the aforesaid rotary knife assembly is coupled with a rotary knife assembly which includes the same number of securely fixed rotary knives. After installing the rotary shaft 10 of the rotary knife assembly in a cutting machine, the rotary shaft 10 is caused to move axially thereof to bring the side face of each rotary knife 12 into pressure contact with that of a respective one of the mating rotary knives to thereby adjust contacting pressure therebetween.
Furthermore, the rotary knife assembly shown in FIG. 3 differs from the previous assembly in that each rotary knife 12, fitted on the reduced-diameter portion, is pressed toward the flange portion of the flange 11 by a coil spring 17; and there is provided a mounting ring 18 disposed around the reduced-diameter portion of the flange 11 to retain each spring 17 in position.
Furthermore, the rotary knife assembly as shown in FIG. 4 includes a fastening bolt 19 threaded through the flange portion of the flange 11 for fastening the flange 11 to the rotary shaft.
For utilizing the rotary knife assemblies as shown in FIGS. 2 and 3, the cutting machine must be provided with a mechanism for moving the rotary shaft 10 in an axial direction, resulting in an increase in cost. The provision of the shaft-moving mechanism lessens the mechanical rigidity and precision of the cutting machine, and hence the cutting machine with such a rotary knife assembly cannot be suitably used to cut a thick product such as steel plates. Therefore, two kinds of cutting machines must be installed when both of thin and thick products must be cut, thereby being uneconomical.
Moreover, the rotary knife assembly as shown in FIG. 4 does not require the shaft-moving mechanism to be provided; the flange 11 must be moved by hand. Therefore, the cutting operation is inefficient and high cutting precision cannot be achieved due to the fluctuation in contacting pressure between the mating knives.